The term motion blur is used to describe the visual streaking effect of moving objects in a still image. In traditional photography, motion blur is the effect of an image changing its position as it is being recorded due to rapid movement that is faster than the shutter exposure time. In computer animation, two-dimensional images can be rendered from three-dimensional models in order to generate successive frames for a movie or video game. In contrast to a physical photograph, computer rendered images can capture a single instant in time, and thus motion blur need not be a part of rendered images. However, without the simulated effect of motion blur, the animation of still images tends to produce movements that seems choppy and segmented to the human eye. For example, computer animation without motion blur can tend to resemble traditional stop-action animation where the model's position is changed between each frame. In order to produce more realistic animations, a motion blur effect can be added by the renderer as each frame is generated. This can have the effect of smearing the still images in each frame according to a direction of motion.